The invention relates to a process to separate a group 8-10 metal/phosphite ligand complex from an organic liquid mixture.
A process to recover rhodium from an organic liquid derived from a hydroformylation process is described in EP-A-355837. In this known process, the rhodium containing liquid is firstly contacted with an ion-exchange resin having bonded ionically thereto an organophosphorous ligand (adsorption of rhodium). Subsequently rhodium is desorped from the thus obtained support by treating the support with a liquid in which the different or preferably the corresponding organophosphorous ligand is dissolved. According to this disclosure the rhodium concentration in the liquid is preferably low, i.e. less than 20 ppm rhodium.
It has been found that, when a phosphite ligand is present in the organic mixture, the phosphite ligand is not recovered by the process according to EP-A-355837. Furthermore the efficiency of the process is low, resulting in that under practical conditions only mixtures can be treated having a low concentration of the group 8-10 metal. According to a preferred embodiment of the process as described in EP-A-355837 the desorption is performed starting with organic mixtures containing dissolved organophosphorus ligands having an ionic moiety. Thus a group 8-10 metal/organophosphorus ligand complex, in which the ligand has an ionic moiety, is at the end obtained. It is however advantageous to directly use the resulting complex in a hydroformylation reaction. Because ligands having ionic moieties are normally used for water soluble catalyst systems and because phosphite ligands are unstable in the presence of water one skilled in the art would not be motivated to use the teachings of EP-A-355837 for the separation of a group 8-10 metal/phosphite ligand complex from an organic liquid mixture.
The object of the invention is a process to separate a group 8-10 metal/phosphite ligand complex from an organic liquid and in which the complex can be recovered and simply reused as a catalyst.
The object is achieved in that the following steps are performed
(1) contacting the organic liquid with a support having bonded thereto an organophosphine ligand and separating the organic mixture which is poor in group 8-10 metal/phosphite ligand complex,
(2) contacting the thus obtained loaded support with an organic solvent and carbon monoxide and separating the thus obtained organic solvent rich in group 8-10 metal/phosphite ligand complex, and
(3) reusing the support obtained in step (2) in step (1).
It has been found that with the process according to the invention group 8-10 metal/phosphite ligand complex can be separated from the organic liquid with a high yield in step (1) and recovered for further use in step (2) in its original, catalytically active form. A further advantage of the process according to the invention is that the group 8-10 metal may be present in the liquid in high concentrations. Another advantage is that the process of the invention regenerates the support for direct reuse.
The use of a group 8-10 metal of the Periodic System of the Elements (New IUPAC notation; Handbook of Chemistry and Physics, 70th edition, CRC Press, 1989-1990) such as rhodium or iridium as part of a homogeneous catalyst system is well known in the art. Typical examples of such processes include the hydroformylation of an unsaturated compound with carbon monoxide and hydrogen to give an aldehyde, the hydrocyanation of unsaturated compounds, the hydrogenation of olefinic compounds and the polymerisation of olefins. In such a process, the group 8-10 metal catalyst generally is stabilized with a ligand.
The organic liquid to be treated in the process according to the invention is for example obtained in a hydroformylation process in which a homogeneous catalyst system is used comprising the group 8-10 metal/phosphite ligand complex. It has been found that the group 8-10 metal/phosphite ligand complex can advantageously be separated from the product stream of such process.
A problem in such hydroformylation processes is the possible accumulation of high boiling compounds in the recirculating catalyst stream. It is therefor necessary to separate the high boiling compounds by means of a purge. For a commercially interesting process it is necessary to recover the catalyst system comprising the group 8-10 metal/phosphite ligand complex from such a purge stream. This is especially advantageous when using valuable group 8-10 metal/phosphite ligand complexes such as for example described in WO-A-9518089.
The group 8-10 metal complex to be recovered by the process according to the invention is present as a soluble group 8-10 metal complex. Without wishing to be bound to any particular theory, it is believed that in step (1) of the process according to the invention the group 8-10 metal complex forms a coordination complex with the organophosphine ligand which is bonded on the support, whereby at least one ligand of the complex is displaced for the organophosphine ligand. Accordingly, it is preferred that at least one exchangeable ligand (L) is present in the complex to be recovered.
Examples of suitable group 8-10 metals are nickel, cobalt, ruthenium, rhodium, palladium, platinum, osmium and iridium. The invention is especially directed to recover rhodium because of its high price.
The mechanism of the first step can, for example for rhodium, be represented as follows: 
in which P1 is the immobilized organophosphine ligand and P2 is the phosphite ligand and L is the exchangeable ligand.
L is for example CO, a phosphine, phosphite, phosphinite, phosphonite, olefin, nitrile, xcex2-diketone or a xcex2-ketoester. L is preferably CO.
The temperature applied during the adsorption of the rhodium complex is generally between 0xc2x0 C. and 150xc2x0 C., preferably between 15 and 80xc2x0 C. and most preferably between 20 and 30xc2x0 C. The temperature is preferably relatively low to minimize degradation of the support and the immobilized complex.
The pressure applied during the adsorption is generally not critical and will in practice be between atmospheric pressure and pressures high enough to overcome any pressure drop in the process equipment.
The adsorption of the group 8-10 metal complex on the support having bonded thereto organo-phosphine ligands can simply be performed by contacting the liquid containing the rhodium complex and the support batchwise, semi-continuously or continuously. When performing the contacting batchwise, an appropriate amount of the support is stirred with the liquid to be treated until a sufficient degree of adsorption is achieved, for example during for about 0,5 to 6 hours. Subsequently, the loaded support is separated from the treated organic liquid with any known solid-liquid separation method. Examples of suitable separation methods are filtration and centrifugation. Preferably, the contacting is performed continuously by passing the liquid to be treated continuously over one or more beds of the support, whereby the separation of the rhodium loaded support from the liquid is inherently facilitated. The bed may be a fixed bed or a liquid fluidized bed. Preferably a fixed bed is used.
The group 8-10 metal complex can subsequently be removed from the loaded support by contacting the loaded support with a suitable organic solvent and carbon monoxide to desorb at least a part of the adsorbed group 8-10 metal phosphite complex from the support (step (2)). Preferably also some hydrogen is present. The desorption of the group 8-10 metal complex is performed in the presence of an organic solvent in which the desorbed group 8-10 metal phosphite complex is soluble. Without wishing to be bound to any particular theory, it is believed that at least the organophosphine ligand of the support is displaced for the carbon monoxid used in step (2), when the group 8-10 metal phosphite complex dissolves in the organic solvent. The temperature applied during the desorption is generally between 0xc2x0 C. and 150xc2x0 C., more preferably between 60xc2x0 C. and 120xc2x0 C.
Suitable solvents are aromatic solvents, for example benzene, toluene, xylene; hydrocarbon solvents, for example heptane, octane, nonane; functionalized solvents, for example ethers, for example methyl tert-butylether or esters, for example ethylacetate. Most prefered solvents are, starting compounds, products and by-products of the (hydroformylation) reaction.
Preferably step (2) is performed at a CO or CO/H2 partial pressure of between 0.1-10 MPa. More preferred step (2) is performed by contacting the loaded support with the organic solvent, which is saturated with CO or CO/H2. Saturation is preferably performed at a pressure of between 2-15 MPa. The molar ratio CO and H2 is preferably between 10:1 and 1:10 and more preferably about 1:1.
The mechanism of the desorption step (2) can, for example for rhodium, be represented as follows: 
Step (2) can be performed batchwise, semi-continuously or continously. When performing step (2) batchwise, the loaded support is stirred with an appropriate amount of the organic solvent in the presence of carbon monoxide until a sufficient degree of desorption is achieved. Contacting time may be for example 0,5 to 6 hours and preferably between 1 and 3. Subsequently, the support is separated from the organic solvent containing the desorbed group 8-10 metal/phosphite complex with any known solid-liquid separation method. Preferably, the desorption is performed continuously over a fixed or liquid fluidized bed of the loaded support. Preferably a fixed bed is used.
The process according to the invention can be carried out batchwise or, preferably, in a continuous process. In a commercial process the reaction is preferably carried out in a continuous mode. When such a type of operation is utilized, at least two columns containing the support are operated parallel, in order to perform step (1) to (3) simultaneously. For example, the liquid mixture to be treated is continuously passed through a first column. After utilizing this support for a predetermined period of time, the flow of the liquid mixture is passed through a second column in order to continue step (1). The first column containing loaded support is subjected to the desorption step (2). After desorbing the rhodium/phosphite complex from the support for a predetermined period of time, the first column can be reused for a subsequent adsorption step (step (3)). This ad- and desorption cycle can be repeated for all the columns resulting in a continuous removal and retrieval of the rhodium/phosphite complex from the organic liquid.
The process according to the invention will be described in more detail for the following preferred embodiments. It shall be evident that the below stated conditions will also be applicable for the above described starting mixtures in a manner clear to one skilled in the art.
A suitable organophosphine ligand, which is bonded onto the support, is in principle any organophosphine ligand which is able to coordinate with the rhodium complex. These organophosphine ligands are well known in the art. A preferred class of organophosphine ligands are monodentate and bidentate organic phosphines. The most preferred organophosphine ligands are monodentate phosphines.
Preferably the support having bonded thereto an organophosphine ligand can be represented with a structure according the following general formula (1) or (2): 
in which m=0 or 1; SP is a linking group; R2, R3, R5, R6 and R7 are the same or different optionally substituted hydrocarbon groups containing 1 to 30 carbon atoms and R1, R4 and R8 are divalent organic bridging groups having 1 to 30 carbon atoms.
The hydrocarbon group of the groups R 2, R3, R5, R6 and R7 are preferably an alkyl, aryl, alkaryl, aralkyl or cycloalkyl group. The hydrocarbon group preferably contains from 1 to 18 carbon atoms and more preferably 1 to 12 carbon atoms. Examples of possible hydrocarbon groups are methyl, ethyl, propyl, butyl, hexyl, cyclohexyl and phenyl.
Preferably, at least one hydrocarbon group of R1, R2 and R3 in formula (1) and at least one hydrocarbon group of R5, R6 and R7 in formula (2) is a phenyl group. More preferably, at least two hydrocarbon groups, and most preferably all the hydrocarbon groups, of R1, R2 and R3 in formula (1) and R5, R6 and R7 in formula (2) are phenyl groups. These hydrocarbon groups may contain one or more substituents. Examples of suitable substituents are alkyl groups, preferably of 1 to 5 carbon atoms, alkoxy groups, halogen atoms, hydroxy, cyano, nitro and amino groups.
Divalent groups R1 and R4 are organic bridging groups containing 1-30 carbon atoms and optionally containing heteroatoms, for example O, N or S. Preferably R1 and R4 are alkylene, arylene, or combinations of an alkylene and an arylene group.
Examples of suitable divalent groups R8 are hydrocarbon groups or hydrocarbon groups whereby two hydrocarbon groups are bridged with an oxygen-, sulphur or nitrogen atom. The hydrocarbon group preferably contains 1 to 16 carbon atoms and more preferably 1 to 12 carbon atoms. Most preferably, R8 is a divalent alkylene radical containing from 2 to 8 carbon atoms, for example ethylene, propylene or butylene.
The linking group SP, is a group which links the phosphine ligand to the support. If m=o a direct covalent bond is present between the ligand and the support, as for example when triphenyl phosphine is bonded to a polystyrene support as is commercially available from Strem Chemicals. The linking group can for example be ionic in nature, as for example described in the afore mentioned EP-A-355837. Preferably the SP group is a divalent covalently bonded group. If a silica support is used the SP-group is preferably a xe2x80x94Si(Rxe2x80x2)(Rxe2x80x3)-group, in-which Rxe2x80x2 and/or Rxe2x80x3 can be an alkyl, alkoxy, aryl or aryloxy group and/or Rxe2x80x2 and/or Rxe2x80x3 is a covalent bond to the silica support. Examples for Rxe2x80x2 or Rxe2x80x3 are methyl, ethyl, isopropyl, isobutyl, butyl, phenyl, methoxy, ethoxy, phenoxy groups.
Preferably monodentate phosphines according to formula (1) are used. Specific examples of the monodentate organophosphine ligand to be used for the organophosphine ligand in the present invention includes triphenylphosphine, tri-p-tolylphosphine, tri-o-tolylphosphine, tri-o-methoxyphenylphosphine, tri-o-chlorophenylphosphine, diphenylisopropylphosphine and diphenylcyclohexylphosphine. The most preferred monodentate phosphine is triphenylphosphine.
The support is, for example, (a) a solid support; (b) an insoluble polymer obtained by polymerisation of a suitable monomer or mixture of monomers and subsequent cross-linking as appropriate; (c) or a soluble polymer on an insoluble support. Examples of suitable polymers are polystyrene, polyethylene, polyvinylchloride, polyvinyl pyridine, polyacrylonitrile and polyacrylates. Suitable cross-linking agents are divinylbenzene, butadiene and diallyl phtalate. The solid support is preferably an inorganic support. Examples of suitable solid inorganic support are silica, polysiloxanes, sand, glass, glass fibres, alumina, zirconia, titania and activated carbon. An especially useful inorganic support is silica.
The supported organophosphine ligands may be prepared using a variety of methods known in the art. The silica supported monodentate phosphine ligands can be prepared by means of procedures as described in Journal of Organometallic Chemistry/87, 1975, page, 203-216 and in Inorganic Chem., 35 (1996) 1814-1819 and as described in the there mentioned references. In addition to the here described methods it is preferred to react all of the non-reacted hydroxy-groups of the silica support with a reactive compound (so-called end-copping) in order to prevent that xe2x80x9cfreexe2x80x9d hydroxy groups are present on the support which may negativelly influence the performance of the process according to the invention. Examples of these reactive compounds are ethoxy trimethyl silane or phenoxy trimethyl silane.
The amount of organophosphine ligand on the support is not critical and is generally between 0.01 and 10 mmol P/g support, preferably between 0.05 and 0.5 mmol P/g support.
It has been found that the process according to the invention can advantageously be used for recovering a rhodium/phosphite complex from an organic liquid containing also high boiling hydroformylation compounds. Such mixtures hereinafter can be obtained in the high boiling purge of a commercial hydroformylation process.
It has been found that with the process of the invention the rhodium/phosphite complex can be recovered in its original active form with a high yield. The recovery of the phosphite ligand is advantageous because of the relatively high cost price of these phosphite compounds. Another advantage of the process according to the invention is that the ligand degradation products of, especially multidentate, phosphite ligands do not adsorb to the support in step (1). This is advantageous because the ligand degradation products will be also separated from the rhodium/phosphite complex by this process.
The high boiler purge is generally removed continuously or intermittently from the hydroformylation system. The purge may be removed either directly from the reactor or, for example, from some point in the catalyst recycle stream.
The invention is therefor also directed to a process for the separation of a rhodium/multidentate phosphite ligand complex catalyst from an organic mixture comprising high boiling hydroformylation compounds.
The concentration of the rhodium complex in the liquid to be treated is not critical. In a hydroformylation high boiler purge, the concentration will generally be higher than 100 ppm rhodium and lower than 2000 ppm rhodium. Preferably, the rhodium concentration is higher than 200 ppm and lower than 1200 ppm. More preferably, the rhodium concentration is equal to or higher than 300 ppm and equal to or lower than 800 ppm.
The concentration of the high boiling compounds in the high boiler hydroformylation mixture may vary from 10-95 wt. %. Preferably, the concentration is between 20-60 wt. %.
The high boiler hydroformylation mixture containing the hydroformylation catalyst and high boiling compounds will generally comprise also 40-80 wt. % of the aldehyde product and 1-5 wt. % ligand degradation products.
After having performed the adsorption step (1), the treated liquid containing the high boiling hydroformylation compounds can be disposed of.
The high boiler purge is preferably removed from a hydroformylation system for the preparation of a linear (or terminal) aldehyde obtainable by hydroformylation of internally unsaturated olefins substituted with one or more functional groups according to formula (3):
CH3xe2x80x94CR=CR10xe2x80x94R11xe2x80x83xe2x80x83(3)
where R9 and R10 are a hydrocarbon group or preferably hydrogen and R11 is a cyanide group or a hydrocarbon group, whether or not substituted with one or more functional groups which contain a hetero atom, for example oxygen, sulphur, nitrogen or phosphorus. Preferably, use is made of internally unsaturated olefins having between 4 and 20 carbon atoms according to formula (3), where R9 and R10 are hydrogen.
Examples of internally unsaturated olefins having between 4 and 20 carbon atoms according to formula (3), where R9 and R10 are hydrogen, are 2-pentene nitrile, 3-pentene nitrile, 3-pentenoic acid and C1-C6-alkyl ester of 3-pentenoic acid. These resulting aldehyde hydroformylation products, in particular methyl-5-formylvalerate, are intermediate products in the preparation of xcex5-caprolactam or adipic acid, which are in turn raw materials for the preparation of nylon-6 and nylon-6,6, respectively. Examples of C1-C6-alkyl-3-pentenoate esters are methyl-, ethyl-, propyl-, isopropyl-, tert-butyl-, pentyl- and cyclohexyl-3-pentenoate. Preferably, use is made of methyl- and ethyl-3-pentenoate, because these compounds are readily obtainable. 3-pentene nitrile, 3-pentenoic acid and C1-C6-alkylesters of pentenoic acid may be present in the reaction mixture as a mixture which also comprises 2- and 4-pentenenitrile, 2- and 4-pentenoic acid and C1-C6-alkylesters of 2- and 4-pentenoic acid, respectively.
The multidentate phosphite ligand of the rhodium complex to be recovered preferably has the following general structure: 
where n is 2-6, X is an n-valent organic bridging group and R12 and R13 are independently two organic monovalent aryl groups and/or one divalent diaryl group.
R12 and R13 are preferably monovalent organic groups with 1 to 20 carbon atoms or R12 and R13 form together one divalent organic group having 6 to 30 carbon atoms. Most preferably, R12 and R13 are monovalent aryl groups having 6 to 14 carbon atoms. The different R12 and R13 groups in the ligand may be different. For example in the same ligand some groups R12 and R13 may be one divalent group while other groups R12 and R13 are monovalent groups.
X is preferably an organic group having between 1 and 40 carbon atoms, and more preferably between 6 and 30 carbon atoms. An example of a ligand having a tetravalent organic group is a ligand having a bridging group corresponding to pentaerythritol. Bidentate ligands, having a bivalent bridging group, are most frequently mentioned in the patent literature.
Examples of such phosphite ligands are described in U.S. Pat. No. 4,748,261, EP-A-556681 and EP-A-518241.
When internally ethylenically unsaturated organic compounds, for example 2-butene or 3-pentenoate, are used as a starting material to prepare terminal aldehydes, use is preferably made of a multidentate phosphite ligand that can form a chelate-type complex with the rhodium in the reaction zone. A chelate-type complex is understood to mean that (substantially) at least two phosphorus P atoms of a ligand molecule form a coordinated bond with one rhodium atom/ion. A non-chelate-type complex is understood to mean that only one phosphorus P atom of a ligand molecule forms a coordinated bond with one rhodium atom/ion. The choice of bridging group X of the ligand will determine whether a chelate-type complex can be formed in the reaction zone. Examples of bridging groups that result in a ligand that can form a chelate-type bridging group are for example described in WO-A-9518089.
A preferred ligand for use in the process according to the invention has a 2,2xe2x80x2-dihydroxy-1,1xe2x80x2-binaphthalene bridging group, which bridging group is preferably substituted at the 3 and 3xe2x80x2 positions. This ligand can be represented by the following general formula: 
where Y and Z are substituents other than hydrogen and R12 and R13 are the same or different substituted monovalent aryl groups and/or any one of OR12 and OR13 connected to one phosphorus atom forms an xe2x80x94Oxe2x80x94R14xe2x80x94O-group, where R14 is a divalent organic group containing one or two aryl groups.
The substituents Y and Z are preferably organic groups containing at least one carbon atom, more preferably containing 1-20 carbon atoms.
Preferably, Y and Z are individually selected from the group comprising alkyl, aryl, triarylsilyl, trialkylsilyl, carboalkoxy, carboaryloxy, aryloxy, alkoxy, alkylcarbonyl, arylcarbonyl, oxazole, amide, amine or a nitrile.
For Y and Z, the alkyl group is preferably a C1-C10 alkyl group, for example methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, isobutyl, pentyl or hexyl. An example of a suitable triarylsilyl group is triphenylsilyl and examples of a suitable trialkylsilyl group are trimethylsilyl and triethylsilyl. Preferred aryl groups have 6 to 20 carbon atoms, for example phenyl, benzyl, tolyl, naphthyl, anthranyl or phenanthryl. Preferred aryloxy groups have 6 to 12 carbon atoms, for example phenoxy. Preferred alkoxy groups have 1 to 20 carbon atoms, for example methoxy, ethoxy, tert-butoxy or isopropoxy. Preferred alkylcarbonyl groups have 2 to 12 carbon atoms, for example methylcarbonyl, tert-butylcarbonyl. Preferred arylcarbonyl groups have 7 to 13 carbon atoms, for example phenylcarbonyl. Preferred amide groups contain a C1-C4 alkyl group and preferred amine groups contain two C1-C5 alkyl groups.
Most preferably, Y and Z are individually a carboalkoxyl or a carboaryloxy group, xe2x80x94CO2R, in which R is a C1-C20 alkyl group or a C6-C12 aryl group and preferably a C1-C8 alkyl group. Examples of suitable R groups are methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, isobutyl, phenyl and tolyl. Even more preferably, Y and Z are both the same carboaryloxy and more preferably the same carboalkoxyl group because the resulting ligands are more easily obtainable.
The 2,2xe2x80x2-dihydroxy-1,1xe2x80x2-binaphtalene bridging group can optionally be further substituted with other groups, for example halogen, for example Cl or F or one of the substituents R which may be present on the bridging group as described above.
R12 and R13 are preferably the same or different monovalent aryl groups, and more preferably aryl groups with 6 to 20 carbon atoms. It is to be understood that all four R12 and R13 groups can be different. Preferably all four groups are the same because the resulting ligands are more readily available. Alternatively, OR12 and OR13 (connected to the same P atom) can form an xe2x80x94Oxe2x80x94R14xe2x80x94O-group, where R14 is a divalent group of 6 to 40 carbon atoms containing one or two aryl groups. Preferably, R12 and R13 are monovalent aryl groups, for example phenyl, containing at least one group, R15, other than hydrogen in an ortho position relative to the oxygen atom, where R15 is a C1 to C20 alkyl or C6-C20 aryl group and preferably a C1-C6 alkyl group. Other preferred monovalent aryl groups for R12 and R13 are monovalent fused aromatic ring systems with 2 or more rings having 10-20 carbon atoms. R12 and R13 can optionally be further substituted with for example C1-C10 alkyl, C6-C20 aryl, C1-C10 akoxy or C6-C20 aryloxy groups or halogen groups, for example F, Cl or Br or amine groups.
When the aryl groups R12 and R13 are substituted with at least one R15 group at the ortho position relative to the phenolic oxygen atom, a higher linear selectivity is observed when these ligands are used in a hydroformylation process. Examples of these R15 groups are methyl, ethyl, propyl, isopropyl, isobutyl, tert-butyl or n-butyl. For R15 preferably only one bulky group, having a steric hinderance of isopropyl or greater, is ortho-substituted on the aryl group. When less bulky substituents are used, both ortho positions are preferably substituted with these groups. The preferred R15-substituted aryl group for R11 and R12 is 2-isopropylphenyl or 2-tert-butylphenyl group.
Another preferred class of aryl groups for R12 and R13 comprises fused aromatic ring systems with 2 or more rings having 10 to 20 carbon atoms which do not necessarily have to be substituted at the ortho position (on the carbon atom adjacent to the carbon atom which is bonded to the oxygen atom in formula (5) with groups other than hydrogen. Examples of such fused aromatic ring systems are phenanthryl, anthryl and naphthyl groups. Preferably 9-phenanthryl or 1-naphthyl groups are used. The aromatic ring systems can optionally be substituted with for example the aforementioned substituents, for example at the positions of the ring systems other than the ortho position described above.
Examples where R12 and R13 are linked to form divalent groups R14 are C6-C25 diaryl groups, for example a 2,2xe2x80x2-diphenyldiyl or 2,2xe2x80x2-dinaphtyldiyl group.
These ligands may be prepared using a variety of methods known in the art; see for example descriptions in U.S. Pat. No. 4,769,498; U.S. Pat. No. 4,688,651 and J. Amer. Chem. Soc., 1993, 115, 2066.
The 2,2xe2x80x2-dihydroxy-1,1xe2x80x2-binaphthalene bridged organic bidentate phosphite compounds according to the invention can be prepared with the 3- or 3,3xe2x80x2-substituted 2,2xe2x80x2-dihydroxy-1,1xe2x80x2-binaphthalene bridging compounds. The binaphthol bridging compounds can be prepared by means of procedures as described in Tetrahedron Lett. 1990, 31(3), 413-416 or in J. Am. Chem. Soc. 1954, 76, 296 and Org. Proc. Prep. International, 1991, 23, 200. The phosphite compounds can be prepared by using the process described in the aforementioned U.S. Pat. No. 5,235,113 to couple these binaphthol bridging compounds with phosphoro-chloridites, (R12O) (R13O)PCl, prepared by treating R12OH and/or R13OH with PCl3.
The catalyst system used in the process according to this invention can be prepared by mixing a suitable rhodium or iridium compound with the phosphite ligand, optionally in a suitable solvent, in accordance with well-known complex-forming methods. The solvent will generally be the solvent used in the hydroformylation. Suitable rhodium compounds are for example hydrides, halides, organic acid salts, acetylacetonates, inorganic acid salts, oxides, carbonyl compounds and amine compounds of these metals. Examples of suitable catalyst precursors are Rh(OAc)3, Rh2O3, Rh(acac) (CO)2, Rh(CO)2(DPM), [Rh(OAc) (COD)]2, Rh4(CO)12, Rh6(CO)16, RhH(CO) (Ph3P)3, [Rh(OAc) (CO)2]2, and [RhCl(COD)]2, (where xe2x80x9cacacxe2x80x9d is an acetylacetonate group; xe2x80x9cAcxe2x80x9d is an acetyl group; xe2x80x9cCODxe2x80x9d is 1,5-cyclooctadiene; and xe2x80x9cPhxe2x80x9d is a phenyl group, DPM is a 2,2,6,6-tetramethyl-3,5-heptanedionate group). However, it should be noted that the rhodium compounds are not necessarily limited to the compounds listed above.
The molar ratio of the multidentate phosphite ligand to rhodium in the hydroformylation reaction mixture and the high boiler purge to be treated is generally from about 0.5 to 100 and preferably from 1 to 10 and most preferably less than 1.2 (mol ligand/mol metal). Preferably the ratio is higher than 1.05. It has been found that in this range the ligand stability during hydroformylation is optimal and the loss of ligand in the high boiler purge according to this invention is minimal.
The invention is therefore also directed to a process to prepare a linear aldehyde, characterized in that the following steps are performed:
(a) hydroformylation of an (internally) unsaturated organic compound in the presence of a catalyst system comprising rhodium and a multidentate organic phosphite ligand, whereby the hydroformylation reaction mixture contains 1-10, preferably 1.05-1.2 mol multidentate phosphite ligand per mol rhodium,
(b) separating the linear aldehyde from the reaction mixture obtained in step (a) resulting in a fraction containing the linear aldehyde and a fraction containing the catalyst system and high boiling compounds,
(c) purging part of the organic mixture containing the catalyst system and high boiling compounds and recycling the rest to step (a),
(d) separating the catalyst system from the high boiling compounds with the process according to the invention,
(e) reuse of the catalyst system obtained in step (d) in step (a).
The above described preferences regarding hydroformylation starting compound, conditions and catalyst system also apply here. Step (a) is preferably performed as described in for example U.S. Pat. No. 5,527,950, EP-A-712828 or WO-A-9518089. Step (b) may be performed using any separation technique known to a person skilled in the art. Examples of suit able separation techniques are (vacuum) distillation, crystallisation and extraction using a suitable extraction agent.